1. Field of the Invention
This invention relates to recording magnetic media and more particularly relates to writing magnetically encoded data to discrete lands.
2. Description of the Related Art
Hard disk drives (“HDD”) are widely used to store digital data for enterprise data processing systems, computer workstations, portable computing devices, digital audio players, digital video players, and the like. In addition, there is strong economic pressure for HDD to store increasingly more data at lower cost. For example, increasing the data stored in a HDD can reduce the operational costs of a storage subsystem by storing more data in a rack of HDD. In addition, there is demand for storing increasing amounts of audio and video data in portable digital audio and video players.
The HDD stores data on a disk with a surface of magnetic material. A write head magnetically polarizes areas of the magnetic material with one or two polarities to encode either binary zeros or ones. Thus data is recorded as magnetically encoded areas or bits of magnetic polarity. An HDD read head detects the magnetic polarity of each bit or area and generates an electrical signal that approximates the magnetic polarity. The signal is processed to recover the binary data recorded on the magnetic material.
The amount of data that an HDD can store and the cost of storing data is a largely a function of the areal density of the HDD. The areal density is a measure of the bits of data encoded per unit area. For example, areal density may be measured as gigabits of data per square inch (Gb/in2). The HDD typically stores more data as the areal density increases. In addition, the cost per byte of data stored typically decreases as the areal density increases. Therefore, increasing the areal density of a HDD is highly desirable.
The areal density of the HDD is dependent in part on the strength of a magnetic field generated by the write head that polarizes the magnetic material. Generally, a stronger magnetic field is able to write data with a higher areal density. The strength of the magnetic field is limited in part by the size of the write head. For geometric reasons larger write heads can produce larger magnetic fields and gradients needed for greater areal densities.
Unfortunately, larger write heads write to larger areas of magnetic material, decreasing areal density. In addition, as the areal density increases, the read head increasingly detects the magnetic polarities of adjacent areas of magnetic material along with the magnetic polarity of the area of magnetic material being read. The magnetic polarities of adjacent magnetic material areas are a component of noise. Noise includes background phenomena that are added to the read head signal that are unrelated to the data bit being read. As the areal density increases, the noise increases, increasing the difficulty of recovering data from the read head signal.
HDD have been constructed with a plurality of discrete radial areas of raised magnetic material referred to herein as tracks or lands. The lands are separated by grooves that may not include magnetic material and that are recessed from the read head. The grooves do not store magnetic data and so are the source of little noise while the read head reads data from the lands. As a result, data is more easily recovered from HDD with discrete lands as the noise from the grooves is reduced.
Unfortunately, the size of the write head is restricted by the size of the lands and grooves. The radial width of the write head cannot be so large that it polarizes an adjacent land while polarizing a target land. Therefore, although the use of discrete lands increases areal density, discrete lands may also limit areal density by limiting the size of write heads for writing magnetically encode data to the lands.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that write magnetically encoded data to discrete lands using a write head with a radial width greater than the radial width of each land. Beneficially, such an apparatus, system, and method would increase the areal density of data written to a HDD.